Method for selectively coating articles

ABSTRACT

ARTICLES TO BE SELECTIVELY COATED, ARE CONVEYED THROUGH A COATING STATION BY A TAPE WHICH SERVES ALSO TO MASK AREAS OF THE ARTICLES WHERE COATING IS NOT DESIRED. THE TAPE IS IN THE FORM OF AN ENDLESS BELT AND COATING MATERIAL IS CONTINUOUSLY REMOVED FROM THE TAPE SO THAT EACH ARTICLE TO BE COATED IS PRESENTED WITH A CLEANED PORTION OF THE TAPE AS A MASK. AUTOMATIC APPARATUS IS PROVIDED TO ALTERNATELY RAISE AND LOWER SECTIONS OF THE TAPE OVER A SUPPORT TRACK FOR THE ARTICLES IN COORDINATION WITH FEED-   ING AND ACCUMULATING DEVICES TO BRING PARTS INTO AND OUT OF ENGAGEMENT WITH THE TAPE.

June 6, 1972 J. M; KEATING METHOD FOR SELECTIVELY COATING ARTICLES 4 Sheets-Sheet 1 Original Filed Dec. 26, 1968 INK/EN r09 J. M. T/NG Arr RNEY June 6, 1972 J. M. KEATING 3,667,989

METHOD FOR SELECTIVELY COATING ARTICLES Original Filed Dec. 26, 1968 4 Sheets-Sheet June 6, 1972 J. M. KEATING 3,667,989

METHOD FOR SELECTIVELY COATING ARTICLES Original Filed Dec. 26, 1968 4 Sheets-Sheet :5

June 6, 1972 J. M. KEATING 3,667,989

METHOD FOR SELECTIVELY COATING ARTICLES Original Filed Dec. 26, 1968 4 Sheets-Sheet 4 F/Gr6 SHUTTLE 52 UP I DOWN TRAVERSING ARM 50 IN OUT f l I ENGAGE I I CLUTCH n2 l m I DISENGAGE I 4 l RAISED I v E OUTPUT ELEV. MECH.42 i LOWERED l t 1 RAISED I INPUT E| Ev. MECH. as I I LOWERED I I i i 1 i i Q t I 4 I E0 t 'tl T5 T5 l 3 F/Gr 7 n4 CAM PROGRAMMER 4 TAPE PART FEED POSITIONER ADVANCE Q ll6- ll8 CONT. CKT. CONT. CKT. CONT. CKT. a9

INPUT OUTPUT lzck ELEvAToR ELEVATOR 4 CONT. CKT- CONT. CKT.

United States Patent O METHOD FOR SELECTIV ELY COATING ARTICLES John M. Keating, Muhlenberg Park, Pa., assignor to Western Electric Company, Incorporated, New York, N.Y.

Original application Dec. 26, 1968, Ser. No. 787,040, now Patent No. 3,587,524, dated June 28, 1971. Divided and this application Aug. 6, 1970, Ser. No. 61,786

Int. Cl. B4411 1/18, 1/52 US. Cl. 117-38 3 Claims ABSTRACT OF THE DISCLOSURE Articles to be selectively coated, are conveyed through a coating station by a tape which serves also to mask areas of the articles where coating is not desired. The tape is in the form of an endless belt and coating material is continuously removed from the tape so that each article to be coated is presented with a cleaned portion of the tape as a mask. Automatic apparatus is provided to alternately raise and lower sections of the tape over a support track for the articles in coordination with feeding and accumulating devices to bring parts into and out of engagement with the tape.

This application is a division of application Ser. No. 787,040, filed Dec. 26, 1968, now Pat. No. 3,587,524, issued June 28, 1971.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to methods of and apparatus for selectively coating articles and more particularly, to automatic continuous masking and conveying of the articles through a coating station.

DESCRIPTION OF THE PRIOR ART In the manufacture of certain articles it is necessary that selected portions of an article be coated, while other portions remain uncoated. For example, in the manufacture of certain types of transistor assemblies, it is necessary to apply a protective coating of silicon dioxide to an active transistor element which is mounted on a platform of a flanged header. However, silicon dioxide deposited on the flange of the header would prevent subsequent welding of a closure to the flange. It becomes necessary, therefore, to shield or mask the flange while exposing the top surface containing the active transistor element to the silicon dioxide during the coating operation.

In the past, the silicon dioxide coating was deposited on the transistor assemblies by: (1) inserting the assemblies in counterbores cut into a surface of a rotating table; (2) manually placing a washer, large enough to cover the flange, over each individual assembly; (3) rotating the table so that the assemblies, with the flange masked by the washer and the top surface exposed through a hole in the washer, passed under a silicon dioxide coating station; and (4) manually removing the transistor assemblies and washers. However, this procedure required manual labor and the loading and unloading of the transistor assemblies and washers, by hand, limited the speed and thereby the output of the coating apparatus. This in turn, added to the cost of coating the assemblies. Another disadvantage of manual operation is contamination of the transistors due to operator handling.

Schemes have been available for automatically masking and conveying articles through a coating medium. But, these schemes have had various shortcomings. Many systems have used masks which required the employment of 3,667,989 Patented June 6, 1972 special registration techniques to coordinate the speed of articles to be masked and the speed of the mask.

Other systems have conveyed articles directly with the mask, but these systems required masks of complex configurations. In a system where a relatively clean portion of the mask is needed to mask each incoming article, a complex mask structure poses significant problems in obtaining a desired degree of cleanliness. Thus, cleaning of complex masks is only practical by subjecting the mask to a series of acid baths and rinses (i.e., wet cleaning systems).

SUMMARY OF THE INVENTION It is an object of the invention, therefore, to provide methods of and apparatus for automatically masking and conveying articles within a coating apparatus to deposit a coating on selected portions thereof.

It is another object of the invention to provide a system wherein a continuous mask functions to convey articles through a coating apparatus so that problems associated with coordinating speeds of articles and masks are reduced.

It is a further object of the invention to provide a mask of simple configuration so that it can be easily cleaned continuously and thus used in continuous operation.

It is a still further object of the invention to provide a system for automatically engaging articles with and discharging articles from portions of a continuous mask without disturbing a coating operation occurring at other portions of the mask.

The foregoing and other objects are accomplished in accordance with the invention by utilizing an endless tape mask having apertures therein shaped to expose and engage selected portions of the article to be coated. Preferably, the articles are supported on a track passing through a coating station for the articles and the mask is positioned along the track. At the input of the coating station, the mask is alternately moved transversely of the path of the articles, between a position enabling an article to be moved into registration with one of the mask apertures to a position wherein the registered mask aperture passes over and engages the article. After each engagement of a mask aperture with an article, the mask is moved to carry the engaged article into and through the coating station.

Advantageously, after exit from the coating station, the mask is moved transversely of the path of travel of the articles to disengage an article and the mask is then passed through a cleaning station so that a clean portion of the mask is presented to each article to be coated.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, advantages and features of the invention will be apparent from the following detailed description of specific examples and embodiments thereof, in which:

FIG. 1 is an isometric view of a transistor subassembly which is to be coated by the apparatus of FIG. 3;

FIG. 2 is a partial isometric view of an endless tape mask and a support track showing the masking of a plurality of the subassemblies of FIG. 1;

FIG. 3 is an isometric view of an apparatus, utilizing the endless tape of FIG. 2, for coating transistor subassemblies in accordance with certain features of the invention;

FIG. 4 is an isomertic view of an input end of the apparatus of FIG. 3;

FIG. 5 is an isometric view of an output end of the apparatus of FIG. 3;

FIG. 6 is a time versus function chart schematically illustrating cooperation between various elements and steps of the invention; and

FIG. 7 is a schematic diagram of an automatic control system for the apparatus of FIG. 3.

DETAILED DESCRIPTION Illustratively, the invention will be described in connection with the selective coating of a transistor subassembly. However, it is to be understood that this is only for purposes of explanation and that the invention has applicability to the selective coating of various other type components.

Referring to FIG. 1, there is shown a transistor subassembly, designed generally by the numeral 10, which includes a header designated generally by the numeral 12, an active transistor chip 14 and a plurality of leads 16- 16. The header 12 includes a raised platform 18, a flange 20 and a plurality of terminals 22-22. The transistor subassembly 10 is coated with silicon dioxide on the entire top of the platform 18 and the transistor chip 14 but not on the surface of the flange 20.

Referring now to FIG. 2, the flange 20 is shielded r masked by covering the flange with a tape mask, designated generally by the numeral 24. The tape 24 is made with drive perforations 26-26 which, advantageously, are identical in size and spacing to perforations in 35 mm. motion picture film. Consequently, all tooth sprockets used for the control and movement of the tape 24 have dimensions to suit 35 mm. motion picture film perforation spacing. In addition, the tape 24 is perforated along its center line with a plurality of evenly spaced masking apertures 28-28. The masking apertures 28-28 are large enough to fit over the raised platform 18 of the subassembly but small enough so that the tape 24 shields the flange 20.

Coating of the subassemblies 10-10 is accomplished by permitting silicon dioxide to condense on the surfaces of the subassemblies when the subassemblies are placed into an atmosphere containing gaseous silicon dioxide. The tape mask 24 prevents condensation of silicon dioxide on the flanges 20-20 but, of course, the tape mask 24 becomes coated with silicon dioxide.

The tape mask 24 is operated as an endless belt arrangement and, in order to continually have a properly conditioned mask available for the articles, successive portions of the mask are cleaned after each exposure to the coating operation. Silicon dioxide is soluble in hydrofluoric acid, but is is preferable to use a dry cleaning technique so that the maintenance of acid baths and rinses is not required. It is, therefore, desirable to keep the configuration of the mask 24 as simple as possible so that the mask can be readily cleaned by dry abrasive techniques.

Since the tape mask 24 must also be able to withstand repeated cycling, it is important, in this particular use of the invention, that the tape have good wear characteristics. A preferred material in this case is stainless steel.

Referring now to FIG. 3, there is shown a coating machine, designated generally by the numeral 30, for auto matically masking and coating the'subassemblies 10-10. The machine 30 includes a vibratory feeding and storage magazine 32, built in accordance with U.S. Pat. 3,194,392 issued to R. W. Manderbach on Aug. 13, 1965, a support track 34, a positioner, designated generally by the numeral 36, an input elevator mechanism, designated generally by the numeral 38, a coating station 40, an output elevator mechanism, designated generally by the numeral 42, an accumulating magazine 44, similar to magazine 32, a cleaning station, designated generally by the numeral 46, and the endless tape mask 24. The magazine 32 feeds the subassemblies 10-10 onto the support track 34 along which each subassembly can be propelled to a position beneath one of the masking apertures 28-28 in the tape mask 24. A portion of the tape mask 24 is raised and lowered over each of the subassemblies 10-10 by the input elevator mechanism 38 so that each of the raised platforms 18-18 protrude through and are engaged by one of the apertures 28-28, while the flanges 20-20 remain covered beneath the tape. The tape 24, and the subassem- 4 blies 10-10, are pulled through the coating station 40 to the output end of the machine where the output elevator mechanism 42 lifts a portion of the tape 24 from the subassemblies 10-10 permitting them to be pneumatically propelled into the magazine 44.

The cleaning station 46 utilizes rotating brushes 48-48 to remove silicon dioxide from the tape 24 as the tape is returned to the input end of the machine 30. The silicon dioxide is a material which is diflicult to remove by brushing and the simple configuration of the tape 24 facilitates the cleaning.

Referring now to FIG. 4, the subassemblies 10-10 to be coated are fed onto the support track 34 from the magazine 32. The subassemblies 10-10 are fed along the track by a conventional escapement-type feed mechanism (not shown), one at a time to a spring stop 49. The subassemblies 10-10 are then engaged and moved further by the positioner 36 so that each of the subassemblies 10-10 is aligned with one of the masking apertures 28-28 of the tape 24. The positioner 36 includes a traversing arm 50 which is arranged for limited rotation about its own axis in order that an attached shuttle 52 can be raised or lowered as required. Longitudinal movement of the traversing arm 50 by a cylinder 54 results in rotation movement of the arm as a result of a translating cam arrangement (not shown).

The positioner 36 is constructed and mounted so that when the shuttle 52 is down, the shuttle is engaged with one of the subassemblies 10-10. When the shuttle 52 is up, the shuttle can be moved parallel to the track without striking the subassemblies 10-10. At one limit of the longitudinal travel of the arm 50, the shuttle overlies the spring stop 49 so,that the shuttle can engage one of the subassemblies 10-10 that is adjacent the stop. At the other limit of the longitudinal travel of the arm 50 the shuttle 52 places one of the subassemblies 10-10 into alignment under one of the masking apertures 28-28 in the tape 24.

Further understanding of the structure and operation of the positioner can be had by referring to patent No. 3,435,943 filed on Aug. 2, 1967 in the name of A. F. Johnson, and assigned to the same assignee as the present application.

The portion of the tape 24 traversing through the coating station 40 which resides between the elevator mechanism 38 and the elevator mechanism 42 (FIG. 3) lies almost adjacent the track 34, as shown in FIG. 2'. The tape 24 is held above the track 34 only by the thickness of the flanges 20-20 (FIG. 1). .When the close spacing between the tape 24 and the track 34 exists, the subassemblies 10-10 cannot be passed into the desired position between the tape and the track.

In order to overcome this difliculty, successive portions of the tape 24 are lifted at the input end of the machine 30 in order to facilitate engagement of the subassemblies 10-10 with the tape 24. This lifting is accomplished by the input elevating mechanism 38. The elevating mechanism 38 includes an actuating air cylinder '70, a support plate 72 attached to the piston of the cylinder and a support bar 74 fixed to the support plate 72 which is con strained to move in a vertical direction by guide posts 76-76.

Also included in the mechanism 38 are a tension sprocket 78 and an idler roller 80, which holds the tape 24 against the sprocket 78. Both the sprocket 78 and the roller 80 are rotatably mounted on the support bar 74.

Attached to a shaft 82 of the tension sprocket 78 is a friction pulley 84 over which a friction belt 86 is passed. The belt 86 is held under tension by adjustable clamps (not shown) so that a predetermined drag is applied to the sprocket 78, in order to maintain a desired tension in the tape 24.

An isolator sprocket 88 is provided between the sprocket 78 and the coating station 30. The sprocket 88 functions to isolate the motion imparted to the tape 24 by the elevator mechanism 38 from the portions of the tape which are within the coating station 40 so that the coating operation remains substantially undisturbed.

As will be further described in detail below, a photoelectric detector 89 is provided to sense the presence of the apertures 2828 in a desired location so that the subassemblies 10 can be properly engaged with the apertures. A conventional switch 90 is provided to detect the absence of one of the subassemblies 1010 from any of the apertures 2828.

Referring now to FIG. 5, the output elevating mechanism 42 raises and lowers successive portions of the tape 24 so that the subassemblies 10-10 may be disengaged therefrom. Similarly to the mechanism 38, the mechanism 42 includes a cylinder 91 which moves a support plate 92, guided on posts 94-94, which plate is attached to a support bar 96 on which a sprocket 98 and an idler 100 are rotatably mounted. When the elevator mechanism 42 is raised, an air jet 101 blows one of the subassemblies 10-10 from the associated aperture 28. The ejected subassemblies are then accumulated within the magazine 44.

An isolator sprocket 102 is hingedly mounted within a mounting assembly, designated generally by the numeral 103, on a spring-biased bracket 104. The hinged mounting of the sprocket 102 facilitates changing of the tape 24 for maintenance purposes. The sprocket 102 also functions as a driving sprocket along with the sprocket 98 to propel the tape 24 through the machine 30.

Sprockets 98 and 102 are interconnected with a belt 106. The belt 106 is propelled through a set of gears 108108 which is in turn rotated by a belt 110 driven by an electromagnetic clutch 112 propelled by a conventional motor (not shown).

OPERATION The overall operation of the machine 30 can best be understood by referring alternately to FIGS. 3, 6 and 7. The subassemblies 1010 are fed from the magazine 32, one at a time, to the spring stop 49 after a cam programmer 114 begins a sequence of operations, the first of which is actuation of a part feed control circuit 116.

A discussion of the cyclic operation of the machine 30, as represented schematically in FIG. 6, can begin when one of the subassemblies 1010 is stopped against the spring stop 49.

At a time t the shuttle 52 is lowered over the subassembly 10 by an appropriate function of a positioner control circuit 118 which is also operated through the cam programmer -114. The arm 50 of the positioner 36 begins moving the shuttle inwardly toward the coating station 40. Movement of the traversing arm 50 is also controlled by the positioner control circuit 118.

At time 1 the input elevator mechanism 38 moves from a lowered position to a raised position. The control of the elevator mechanism 38 is accomplished by an input elevator control circuit 120. Additionally, at the time t the traversing arm 50 is still progressing inwardly toward the coating station 40 with the shuttle 52 being down where it is engaged with the subassembly 10 so that the subassembly 10 is being urged toward the input elevator mechanism 38.

At time t the traversing arm 50 has reached the limit of its inward motion and the shuttle is raised so that it no longer is engaged with the subassembly 10. It should be noted that the input elevator mechanism 38 is still in its raised position. This arrangement permits the shuttle 52 and the associated subassembly 10 to fit between the tape 24 and the track 34.

At time t the traversing arm 50 begins its outward movement under control of the positioner control circuit 118. The shuttle 52 is still up so that it can clear a subassembly 1010 which has been conveyed to a position against the spring stop 49, under control of the part feed control circuit 116.

At time t the input elevator mechanism is lowered, and one of the apertures 28 becomes engaged with the platform 18 (FIG. 1) of the subassembly 10. The traversing arm 50 is still moving outwardly at time t; with the shuttle 52 in the up position.

Since the tape 24 is now engaged with the subassembly 10, it is desirable to move the tape 24 longitudinally so that the subassembly 10 is urged toward the coating station 40. Since the subassemblies 10--10 are conveyed as well as masked by the tape 24, problems usually associated with registry of a mask and articles to be masked are greatly reduced.

At time t the clutch 112 is engaged to advance the tape 24. During the time that the clutch 112 is engaged, the tape 24 is moved longitudinally along the track 34. Engagement of the clutch is controlled through a tape advance control circuit :122.

The longitudinal travel of the tape 24 is terminated at time t and time t is determined by a signal from the photoelectric detector 89. The detector 89 scans the tape 24 continuously. The detector 89 is positioned in such a way that a signal is generated whenever one of the apertures 28 is in alignment with the input elevator mechanism 38 such that the positioner 36 will place one of the subassemblies 10-10 directly under the aperture 28, when the input elevator mechanism 38 is raised.

Automatic control of the machine 30 is released from the cam programmer 114 after the clutch 112 is engaged. The clutch 112 is allowed to remain engaged until the tape advance control circuit 122 receives a signal from the detector 89 indicating that one of the apertures 2828 is properly positioned. A signal from the detector 89 is effective to disengage the clutch 112, thereby stopping the tape 24, and in addition the signal causes the cam programmer 1-14 to begin a new cycle of operation.

Thus, cyclic operation of the positioner 36, the input elevator mechanism 38 and the clutch 112 results in the subassemblies 1010 being moved from the magazine 32 into the coating station 40 in a spaced and masked state.

Within the coating station 40, the subassemblies 10-10 are exposed to silicon dioxide in gaseous form. Because the subassemblies 1010 are at substantially ambient temperature, the silicon dioxide condenses onto the exposed surface of the subassembly. Silicon dioxide also condenses onto the tape 24 within the coating station 40.

After emerging from the coating station 40, the subassemblies 1010 are continuously indexed longitudinally along the track 34 by the tape 24, until they reach the output elevator mechanism 42. The output elevator mechanism 42 is operated simultaneously with the input elevator mechanism 38 under control of an output elevator control circuit 124.

At time t the output elevator mechanism 42 is raised and one of the subassemblies 1010 is discharged from its associated aperture 28 by air blown from the jet 101. After ejection from the tape 24, the subassemblies 1010 are accumulated within the magazine 44.

Portions of the tape 24 emerging from the input elevator mechanism 42 are coated with sliicon dioxide. In order for these portions of the tape 24 to be suitable for masking, it is desirable that the silicon dioxide be removed therefrom. Removal of the silicon dioxide is accomplished within the cleaning station 46 wherein the portions of the tape are continuously indexed past a plurality of rotating brushes 48-48 which brush away the silicon dioxide coating.

Portions of the tape emerging from the cleaning station 46 are in suitable condition for serving as masks for the subassemblies 1010 when they are merged with subassemblies at the input elevator mechanism 38.

Except as tthey are combined with each other into an inventive system, the aforedescribed control circuits are of conventional configuration and can readily be constructed by ones skilled in the art of assembling such ,circuits. Therefore, the circuits are not described in detail.

What is claimed is: 1. A method for conveying articles having a raised portion through a coating station and for selectively masking portions of the articles so that only the raised portions are coated, which comprises the steps of:

alternately changing a relative positioning between portions of the articles to be masked and successive portions of an endless tape mask from an enlarged spacing, large enough to allow the articles to be moved freely of the mask, to a position in which the portions of the articles to be masked are adjacent the mask;

aligning each of the raised portions of the articles with one of a plurality of apertures in the mask when the enlarged spacing exists so that the raised portion of the article will protrude through and be engaged with the aperture when the portion of the article to be masked becomes adjacent the mask;

moving the mask so that the articles engaged with the mask are conveyed through the coating station in timed relationship with the step of alternately changing a relative positioning; and

8 continuously cleaning a coated material from successive portions of the mask so that each of the articles is provided with a cleaned portion of the tape mask.

2. The method of claim 1 wherein the position changing step is accomplished by alternately raising and lowering successive portions of the mask with respect to suecessive ones of the articles to be coated.

3. The method of claim 1 wherein the cleaning step is accomplished by brushing the coating material from the mask.

References Cited UNITED STATES PATENTS 3,006,316 10/1961 Wullenwaber 118301 3,296,999 1/1967 Gamble 1182 2,505,063 4/1950 Palermo 1l8301 ALFRED L. LEAVITT, Primary Examiner M. F. ESPOSITO, Assistant Examiner US. Cl. X.R.

Ul"=HT?D TA TE ATENT @EFEQE QERTH EQATE @REQEI Patent No. 39 79 Dated June 2 972 gmtemmqs) John MD Keating Golumn 3;, line LLS "is first occurrence should be it o Column L line 25 "rotation" should be -=-=rotational Column L line 73 Due to a printing error the following paragraph was omitted from the patents --Actuating the cylinder 70 results in a raising or lowering of the sprocket 78 and the idler 80. The idler 80 is preferably formed of a resilient material such as nylon so that some resilient compressive force can develop between the idler and the sprocket 78 with the I tape 214. being compressively captivated between the sprocket T8 and the idler 80 a raising or lowering of them will result in the captive portion of the tape 214. being correspondingly raised and lowered q Column 6 line 73 tthey should be --they-O Signed and sealed this 27th day of 197 3.

(SEAL) At'test:

EDENARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

